Uniform excitation of laser gas is of particular importance in the case of molecular gas lasers such as CO2 and CO lasers where over pumping can lead to localized degradation of optical gain in the gas. In addition, electrically pumped gas lasers in general may suffer from instabilities that form under high pulse energy conditions. Electrical discharge instabilities may lead to intense arc discharges which may damage the laser electrodes or at the very least render the optical quality of the gas discharge gain medium useless for producing a high mode quality laser beam. Establishing very high initial gas discharge uniformity is of paramount importance for pulsed, high energy, gas lasers in order to increase the amount of energy that may be deposited into the gas before the inevitable onset of gas discharge instabilities.
Traditionally, gas lasers have been operated in continuous wave (cw) mode at low gas pressures (10 to 100 torr) or as pulsed lasers at high gas pressures (300 to 760 torr). At low gas pressures gas lasers typically have small transverse gas discharge dimensions (1 to 4 mm) to produce some degree of discharge uniformity by relying on high rates of ambipolar diffusion in the laser plasma. In addition, extra helium is added to the gas mixtures of low pressure gas lasers to improve discharge uniformity by further enhancing ambipolar diffusion. At high gas pressures, gas lasers usually have transverse discharge dimensions that are too large to allow ambipolar diffusion to be practical. High pressure gas lasers have traditionally used specially profiled electrodes to achieve very good uniform electric field conditions where the gas discharges occur.
Profiled electrodes typically utilize a central region with a flat, parallel, electrode geometry in conjunction with profiled electrode regions chosen to gradually reduce the electric field strength on both sides of the central region while introducing only a minimal amount of electric field distortion in the central region. The gas discharge in a profiled electrode assembly is usually confined to the central region and will have either a square or rectangular cross-section. Unfortunately, the lowest order optical mode of a laser will most likely have a cross-section that is either circular or elliptical and is not a good match for the discharge cross-section of a profiled electrode assembly. About 20% of the energy deposited into the gas discharge of the profiled electrode assembly will not be in the optical cavity of the laser and will be wasted.
Rather than flat electrodes which waste energy, curved electrodes can be used around a cylindrical cross-section. The resulting electric field will fill the optical mode cross-section but unfortunately will be non-uniform. At high gas pressure the RF current flowing through the laser gas of the curved electrode assembly will bunch up on both sides of the optical mode cross-section and largely bypass the gas in the center of the electrode assembly. The non-uniformity of the field will also reduce the efficiency of the laser assembly. It is known that if both the dielectric and the electrodes are carefully shaped, an electrode assembly that does produce a uniform gas discharge with a cross-section that does match the cross-section of the lowest order mode of a laser can be created. However, this process can be very complicated to manufacture.
Thus, a need still remains for a simpler fabrication method of an efficient laser electrode assembly. In view of the growing importance of energy-efficient high-power lasers, the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.